Alloy steel



Patented Dec. 27, 1938 UNITED STATES PATENT OFFICE 2,141,389 ALLOY STEELWilliam Herbert signor to Thos. Firth Hatfield, Sheflield, England, as-

& John Brown Limited,

Sheffield, England, a British company 3 Claims.

This invention comprises improvements in or relating to alloy steelsexhibiting good mechanical properties at elevated temperatures.

Numerous alloy combinations have been proposed for obtaining improvedproperties of constructional materials for use at elevated temperatures.

It is generally recognized that, as regards steels, the richer alloys ofthe austenitic type, containing sufficient proportions of chromium,nickel and other elements to render them for practical purposes stablein the austenitic or austenito-martensitic condition, show superiorproperties to ordinary alloy steels when tested in the range oftemperature round about 500 C. and upwards. In this connection, theaddition of tungsten for improving high temperature performance ofchromium-nickel steels is well establlshed.

The present invention provides an austenitic nickel-chromium alloy steelsuitable in particular as a constructional material for use at elevatedtemperatures, and characterized in that it contains as essentialconstituents a small proportion of titanium and a relatively higherproportion of cobalt.

More specifically the invention comprises an alloy containing 20-40%nickel, 6-20% chromium, 10-30% cobalt, 1-5% titanium, up to 0.6% carbonand the remainder iron.

The improved alloy may also embody small proportions of other elementssuch as manganese and silicon normally used in alloy steel production.It is also within the invention to replace part of the nickel up to sayby manganese, and to replace part of the chromium up to say 3% bysilicon. The following is an example of an alloy composition accordingto the invention and of the properties possessed thereby:-

Analysis Per cent 0.1 0.36 1.14 30.05 9.66 20.43 '1 2.08 Fe Remainder.

Treatment:

Air cooled 1050" C. and reheated to 650 C.

Tests at ordinary temperatures:

Yield point 32 tons/sq. in. Maximum stress 59 tons/sq. in. Elongation31%.

Reduction of area 41%.

Tests at 600 0.-

Short time test:

(Rate of pull 0.12" per minute.) Ultimate strength 35-tons/sq. in. Longtime test:

(Hatfield time-yield test) time-yield value 15.5 tons/sq. in.

I claim:

1. An austenitic nickel-chromium alloy-steel suitable in particular as aconstructional material for use at elevated temperatures and comprising20-40% nickel, 6-20'% chromium, in excess of 10% and up to 30% cobalt,1-5% titanium, a material amount not exceeding 0.6% carbon, and theremainder iron with a minimum of 20%.

2. An austenitic nickel-chromium alloy steel suitable in particular as aconstructional material for use at elevated temperatures and comprisingabout 30% nickel, 10% chromium, 20% cobalt, 2% titanium, 0.1% carbon andthe remainder iron. v

3. A constructional aterial for use at elevated temperatures comprisingan austenitic nickel-chromium alloy steel containing about 30% nickel,10% chromium, 20% cobalt, 2% titanium, 0.1%carbon and the remainderiron, the steel being in the condition which results from heat treatmentby air cooling at about 1050 C. and reheating to about 650 C., andhaving a yield point of about 32 tons per square inch, a maximum stressof about 60 tons per square inch and a percentage elongation of about31.

WILLIAM HERBERT HATFIELD.

